It is necessary to protect a pressure vessel or storage tank from over-pressurization when filling the pressure vessel with a liquid from a source that is capable of achieving a higher pressure than the maximum permissible pressure of the vessel or storage tank.
Pressure vessels are equipped with pressure relief devices such as relief valves or rupture disks which are activated when the maximum permissible pressure in normal operation is exceeded or when other unfavorable conditions exist. A pressure relief device maintains the pressure in a vessel at the permissible level by discharging fluid from the vessel when the pressure setting of the pressure relief device is exceeded. The liquid source, for example a tank truck that delivers and dispenses liquids, however, may supply an excess amount of fluid at a high pressure such that the relief valves are not capable of protecting the vessel from the excessive pressure.
Liquefied gases, such as liquid nitrogen, oxygen, argon, methane, carbon dioxide and others, are stored and transported at low temperatures. Typically, the liquefied gases are stored and transported in pressure vessels equipped with vacuum or foam insulation and a relief valve or rupture disk pressure relief device. In addition to the issues stated above, the pressure relief devices are unable to relieve the pressure generated in the top of the vessel and relief piping, which is due to vapor produced by evaporation of the liquid as it is delivered to the vessel by a highly powerful pump, when the vessel becomes completely filled with pressurized fluid. Such powerful pumps may be found on some tank trucks. In each of the above instances, it is crucial to avoid exceeding the maximum permissible pressure of the vessel. This may be achieved by closing the filling piping and/or reducing the flow rate of the fluid from the source into the filled pressure vessel. As such, a quick closing shut-off valve is desirable.
Quick closing shut-off valves are installed at the inlet of pressure vessels to protect the pressure vessels against over-pressurization by closing when the pressure in the vessel exceeds a predetermined level. Quick closing shut-off valves are particularly useful with storage tanks for cryogenic liquids due to the high pressure and high flow rate pumps mounted on many cryogenic liquid tank trucks and also due to the expansion of the cryogenic fluids which occurs due to evaporation as they flow to the vessel being filled.
A common type of prior art quick closing shut-off valve, however, is fitted with a compressed spring that is secured with a latch. The latch is released when the pressure in the vessel reaches the maximum level to shut-off the flow of the fluid into the vessel. Re-opening the flow of the fluid into the vessel requires re-compressing the spring and locking the valve in the open position with the latch. This resetting of the valve is time-demanding and requires special tools to compress the spring. In addition, the design of this prior art quick closing shut-off valve is complicated with passive resistances in the releasing mechanism that are not reliable.
German publication DIT 25 50 558 A1, German Patent No. DE 100 11 674 A1 and United Kingdom published patent application number GB 2 355 510 illustrate valves for reducing pressure, shutting off flow and regulating flow, respectively. Each of the valves features a sliding piston or plunger that is housed within a valve body. The valve body includes a liquid inlet and a liquid outlet. The piston or plunger is moved to restrict or eliminate the flow of liquid from the valve inlet to the outlet.
Each of the three valves, however, suffers from disadvantages with regard to use in protecting pressure vessels. More specifically, the valve of German publication DIT 25 50 558 A1 is not suitable for protecting pressure vessels where fast restoration of operating conditions is desirable after relief of pressure from the vessel. The closing of the valve of German Patent No. DE 100 11 674 A1 takes place magnetically when a pressure decrease occurs. Conversely, the liquid flowing to the valve must be at a certain pressure level to open the valve. Such an arrangement is not suitable for protecting pressure vessels against excessive pressure. The valve of United Kingdom published patent application number GB 2 355 510 is complicated and costly. In addition, the valve requires a pressure impulse to open the valve. The creation of such an impulse requires additional equipment capabilities.
Other known automatic shut-off valves have complicated mechanisms for shutting-off fluid flow, usually including springs, balls or other moving parts that are difficult to produce, wear quickly with use and require frequent maintenance.
As a result, the prior art quick closing valves suffer from a number of disadvantages with regard to shutting off the flow of fluid, particularly of liquefied gases, into a pressure vessel.
Accordingly, it is an object of the present invention to provide a quick closing shut-off valve that automatically closes when the pressure in a vessel being filled reaches a predetermined level.
It is another object of the present invention to provide a quick closing shut-off valve that automatically opens when the pressure in a vessel decreases from the predetermined level.
It is still another object of the present invention to provide a quick closing shut-off valve that is economical to manufacture, operate and maintain.